forensic pathology and forensics. it's the study of the human nature. that's the dark side to it. and it is really unfortunate, but we can be pretty mean and nasty. most homeowners would prefer grass to a lawn full of weeds, but the forensic scientists, weeds can tell a story. with the help of a plant biologist and a new high-tech computer program, investigators solve the mystery of the young girl's murder. weekends were typically busy in the mouser household. one saturday morning in 1995, as cathy mouser was leaving for work, she reminded her 14-year-old daughter, genna, that she was grounded for the weekend and wasn't allowed to use the telephone, either.

>> genna was having some behavioral issues. a lot of 14-year-olds, 15-year-olds, might have those kinds of issues when they're growing up, lots of pressures, within the family. she was having such trouble that the family was taking her to counseling. >> cathy returned home from work around 1:00 p.m. and as soon as she tried to open the door, she knew something was wrong. >> mrs. mouser found the front door locked which she said was unusual because usually there's somebody there. she was expecting genna to be there, so the front door would have been unlocked. >> genna wasn't home and she hadn't left a note saying where she went. >> they just figured she was upset and she had basically just walked away, you know, or she was just with one of her friends or -- yeah. >> none of the neighbors saw genna leave or noticed anything suspicious. when genna's stepfather and brother arrived home several hours later, they searched the

neighborhood and called all her friends, but no one knew where genna was. later that night, the mousers called police to report their daughter missing. the next morning, the mousers learned that the nude body of a teenaged girl was discovered in a ditch about 20 miles outside of town. the family identified genna's body at the morgue. >> the reality of her being murdered rather than an accident or -- it didn't hit me. i didn't understand, really, that something like that could happen in my life. it was -- it was hard to deal with and to -- it was just such an unfair act. and i couldn't -- couldn't understand it for a long time. >> the coroner identified the cause of death as strangulation. there were other injuries, as well.

>> in addition to the ligature strangulation marks, she also had evidence of blunt force injury to the head. she had received a blow to the head in the left forehead area and the left temple. >> there were no defensive wounds and no signs of sexual assault. >> the scalp here is brown, about 14 inches in length. >> the soles of the feet were clean in this case and that indicates to me that she certainly was not standing up at the scene where she was found. she certainly did not walk there. >> no injuries. >> the only other findings were some unusual marks on genna's thigh, indentations that were made after death. >> on a living person, these fade very quickly. in this case, these are postmortem pressure marks. they don't tend to fade because the -- the color comes as the blood leaks out of the vessels by gravity after death and it more or less outlines the area

of pressure. and then it stays that way indefinitely until the body decomposes. >> the mousers' telephone records yielded the first clue. despite the fact genna was told not to use the telephone, she called several friends that morning. >> yeah, you should have talked to them. >> really? he's a senior? you'll see him monday. >> around 11:30, genna's conversation with her friend ended abruptly. >> hello? genna? genna? >> one of the last people that she speaks with says that the phone goes dead. genna doesn't call back. her friend pages her a couple of times. genna never calls back. >> police found genna's diary in her bedroom which had an entry from the morning of her murder. >> dear journal, sorry i haven't written you, but i've been pretty busy. things have been going pretty good at school except for the fact that guys don't even know i'm alive half the time. >> the diary expressed a specific interest in two boys.

one was considerably older than genna, a boy she met at a local amusement park. >> he was a young man, about 18 to 19 years old, who was preying on children that were not age appropriate. >> he was older than us. not -- not the best kind of person that you'd probably want to -- want to be with. but he -- there was something that she saw in him that attracted her to him. >> investigators needed to start checking alibis and there was one that almost defied belief. [ male announcer ] this is the age of knowing what you're made of. why let erectile dysfunction get in your way? talk to your doctor about viagra. ask if your heart is healthy enough for sex. do not take viagra if you take nitrates for chest pain; it may cause an unsafe drop in blood pressure. side effects include headache, flushing,

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the mouser family had planned a traditional funeral service for their 14-year-old daughter, genna, until her friend, sarah hollander told them about a conversation the two once had about funerals. >> we got on the topic of funerals. she did not want her funeral to be a sad thing. she doesn't like it when people are sad. she loves to make people happy.

she loves to make people laugh. she did not want her funeral to portray something that she wasn't about. >> so the mousers allowed sara to help plan the funeral service, one that was closer to genna's wishes. doug mouser took his stepdaughter's death particularly hard. he had raised genna since she was 2 years old and treated her like his own. >> she truly did have a great relationship with him and loved him. and he loved her. he was very active in her life. >> in the search for genna's killer, investigators looked inside the mouser's home, but found no clues. >> everything was basically in its place, nothing knocked over or anything to indicate that genna was fighting and screaming as she went out the door. >> this raised the possibility that genna left home voluntarily. >> what the sheriff's department did was try and identify any boys she might have known or

maybe boys she might have left the house with even if she was grounded, maybe she would get in a car with them and drive away. >> police were able to identify the two boys genna mentioned in her diary. both had alibis for the day of the murder. so police turned their attention to the whereabouts of genna's family members. genna's 18-year-old brother, geran, had a solid alibi. >> neighbors have him placed there for an hour, hour and a half or so and that's the time period where genna disappears. >> genna's mother, cathy, was teaching an aerobics class at a local gym, so her alibi collected out, too. genna's stepfather said he went to work for a few hours. when police tried to verify his alibi, they discovered the cameras were turned off that day. >> when he went into the lab, he has to go through a security gate where all of the cars that are coming in are cleared. initially, the person who was in

the booth at the time said they didn't remember seeing him or his car coming through. >> doug mouser couldn't give any description of the security guard. for a man would worked at the lab for a number of years, you would think he could have given more information. >> so doug provided a second alibi. that he bought lunch at a local fast food restaurant. coincidentally the restaurant's security cameras weren't working either. >> if he didn't have bad luck, he would have no luck at all. i can't really imagine you going into places that are supposed to have video cameras and none of them record you. >> it was sort of exasperating, because of snafus if you will. we didn't have any tapes. we didn't have any solid stuff to show that he was there. >> when police looked in doug's car, they found no blood or any evidence suggesting foul play.

and there was no evidence the car had recently been cleaned. but underneath the car, investigators found something trapped in the undercarriage. >> there was a significant quantity of this dried plant material, some of it very large pieces, and those were removed and analyzed later. but had this plant material been there for weeks, you certainly wouldn't expect to find such large pieces of it still attached to the undercarriage. >> could these dried weeds tell investigators anything about genna's murder?

doug mouser told police he was the last person to leave the home on the morning his stepdaughter went missing. he claimed genna was cleaning her bedroom when he left. >> there was no physical evidence that connected him, no hair samples, dna, anything like that. >> there was no physical evidence. none. there was zippo, zero, nil, nada, nothing. >> yet investigators found some suspicious plant material underneath doug's car. which they sent to forensic botanist dr. fred hrusa. he identified the usual

specimens you would expect to find underneath a car, grass, dirt, debris. but he also found large quantities of yellow starthistle, a weed. >> i saw the yellow starthistle and then i saw the small scraps that had been taken off the body. and i was able to compare that to the material that had been collected from the area around the body and also from the trees that were in the overstory above the canyon where the body was found. >> dr. hrusa was looking for what botanists call diagnostic characteristics, unique aspects of the plant that differentiated from others of the same species. dr. hrusa discovered the starthistle under doug mouser's car was identical in development to the starthistle found near genna's body. while this was significant, it wasn't enough to tie doug mouser to the murder. >> the yellow starthistle is not

a rare plant. it is an extremely common plant. so in any given area of -- especially of northern california, and at low elevations, yellow starthistle could be there. >> and with the other flora under the car, it shows that he's been off road. so he could have picked it up anywhere. >> investigators agreed, so they turned their attention to the linear marks found on genna's thigh. >> the marks were made by a manmade object. they were clearly of a shape and appearance that would not be normally found in nature. >> while looking inside doug mouser's car, detective bosma thought he found what caused them. >> the hair on the back of your neck stands up and you're going, this could be one of the marks on her leg. >> but he didn't tell anyone about his discovery. instead, he sent photographs of genna's skin marks to gary robertson, a pioneer in the

field of photogrammetry, to see what he thought might have caused them. robertson wanted to identify the exact size of the marks down to the micromillimeter. so he scanned every autopsy photograph of the marks, which enabled him to create a three dimensional model. >> we're extracting the measurement, say from the left photograph, extracting it from the right photograph, and the computer software merges that into a three-dimensional measurement or a model that we can extract and view later. >> judging from the size and shape, robertson suspected that at least one of the marks was caused by the top part of a seat belt buckle. this was precisely what hans bosma thought, too. but he wanted robertson's independent analysis. >> well, normally, i don't have any information. so i wasn't aware of anything about the vehicle.

>> next, robertson flew to modesto, california, to conduct an experiment in doug mouser's car. he wanted to try to recreate the same skin pattern that was on genna's thigh. he placed a live model, the same height and weight as genna in the back of the vehicle over the rear seat belt buckle. it was a hatch back and one of the back seats was broken and was kept flat. the model remained in the same position for 15 minutes, the time it would have taken to drive from genna's house to the dump site. when the model was photographed, robertson and bosma discovered what caused the other mark on genna's leg. >> when he placed her in there, the -- there's carpet on the back of the seat because it lays flat. so he had a nice carpeted area. the carpet bead folds over as he pulls or pushes her over that

particular area. and that carpet bead was what one of the indentations were on her leg. >> just to make sure, robertson put the model's pictures into his computer and compared them to the marks on genna's leg. it was a virtue match. interestingly, the ripped carpet in the back seat of doug's car was unusual, something you wouldn't find in other cars. >> when he came back and said, i it's a match, boy, we were just ecstatic. we finally are going to be able to nail this guy. now we got him because now we can put genna in the car. >> all the pieces fit together only one way, and that's showing doug mouser guilty of killing genna. >> they didn't theorize it. excuse me. they didn't theorize [ bleep ]. i'd say it on the screen, even in the courtroom.

they didn't have [ bleep ] any theory other than he threw the body, killed her and threw it over the side and that she was in his car because of the mark on her leg. that's all there was. >> based on the forensic botany and photogammetry, doug mouser was arrested and charged with his stepdaughter's murder.

prosecutors wondered, what motivated doug mouser to kill his 14-year-old stepdaughter, genna? >> how can you possibly imagine someone doing something so horrible? i can't imagine it, but it happens, unfortunately, all the time. >> prosecutors found evidence that genna didn't always do what her parents asked. >> she saw a counselor with some regularity. she had oppositional defiant disorder, that she was very defiant, very aggressive, very confrontational with family, with parents. >> the mousers' telephone records provided a possible clue. >> i just got back from the mall. >> on the morning of her death, genna was on the telephone violating her parents' rules. >> his name is scott. >> really. >> he's a senior. >> prosecutors believe doug

caught genna on the phone, lost his temper, and struck her. >> hello? genna? >> prosecutors believe doug's impulsive act of violence threatened his career. >> he couldn't risk an allegation that he hit her, struck her, he was working at lawrence livermore lab and he has security clearance so any criminal record would have been difficult for him and put his job in jeopardy. >> with genna unconscious and not sure what to do, prosecutors think doug panicked and strangled her to death. he removed genna's clothing to eliminate possible trace evidence. when doug pushed genna's body into the back seat of his car, he displaced the carpet. the underside of the carpet and the seat belt buckle left signature marks on her skin that wouldn't disappear since there was no blood flow.

doug chose a dump site 15 minutes away, pulled his car off the road, which picked up the bits of starthistle, the same stage of development that was found on genna's body. prosecutors think doug simply got lucky when the security cameras at both his office and the fast-food restaurant weren't working. but doug made a crucial mistake during his interrogation. he said he used his computer that saturday at the office. but his employer found no evidence that doug logged in. >> they couldn't find any evidence whatsoever that he had done to his computers what he said he did. basically we caught him in a lie. >> doug mouser was tried and convicted of second-degree murder and sentenced to 15 years

to life in prison. he continues to maintain his innocence. >> i -- for me, this is the greatest failure of my life. the only way i live with this situation is that i did the best that i could. i did everything that i could think possible. >> definitely jekyll and hyde personality. at one moment, he's mr. calm and cool. the next moment he's something totally different. >> i think she would be really happy to know that people love her so much to find the real answers to what really happened to her. and she would be happy to know we haven't forgotten about her. >> the case against mouser was largely circumstantial but the photogrammetry helped convince the jury.

>> photogrammetry was the key element and it was used to solve the case. without photogrammetry this case would have gone unsolved. a car runs off the highway into a river. yet the driver is nowhere to be found. for answers, investigators recreated the crash and the evidence revealed a plan almost 20 years in the making. the result of a deadly obsession that ended in tragedy. nick howard was just 18 years old, fresh out of high school and working in his father's car repair business. he was trying to decide what to