it had taken 13 years to arrest sam lopez. ld take another 8 to bring him to trial and just months before that trial began, matt murphy learned that sam had a new defense attorney, someone matt knew very well. >> he's so good and i would be lying if i said my heart was not in my throat. >> sam's defense attorney was the former assistant d.a. who supervised the homicide unit. in fact, he was the original prosecutor who back in 1994 didn't think there was enough evidence to charge sam. not only that, lou was the man who brought matt into the homicide unit. >> lou took me under his wing and trained me how to do homicides. >> what's it like to go up against your mentor? >> it's terrifying. >> neither one of them had ever lost a murder case. but someone's winning streak was about to end. february 10, 2015, 20 years after cathy torrez's murder, sam lopez went on trial. >> at the end of this case, you are going to hold that man accountable for exactly what he did. >> the very first witness matt murphy put on the stand was cathy's mom

last two years. >> reporter: from the beginning, police had suspected cathy's one-time boyfriend sam lopezomething to do with her murder. but they had nothing connecting him to the crime. no witnesses. no dna. and sam had that solid alibi. tina was still married to sam's brother, armando. the two families intertwined, as cathy's family continued to search for answers. >> and then in april of 1997, i got a phone call from mary bennett. >> reporter: cathy's mom. it would be their first conversation of many. mary told daron how she'd seen reports about a new program in orange county centered around investigating cold cases. cathy's case had specifically been mentioned. >> and mary said, "if they're going to use my daughter's murder as publicity for their program, by all means they're going to work it. and it's your job to make sure that that happens." >> reporter: there were no new murders in placentia in 1997, allowing daron to focus his full attention on this old one. >> and because you have -- you have mary bennett and the family, who's persistent, who are very well known and very well lik