this is "nightline." >> tonight breaking news. monster storm. hurricane matthew menacing florida. winds of up to 130 miles per hour raging just offshore. the state's governor with a dire warning. >> unfortunately this is going to kill people. >> mass several states and millions facing what could be the most powerful storm to hit the east coast in more than a decade. plus a murder for hire plot unraveling. one of the hit men cooperating with authorities. will he reveal who hired him to kill this florida professor? the exclusive undercover phone recordings that have investigators closing in on the unlikely suspects. no pom polls here, cheer

twists and the concussion rates are shooting up with them. tonight a former cheer leader with a warning for young athletes. first, the night line five. >> boost, it's about moving forward. not back. it's looking up, not down. it's feeling up, thinking up, living up. it's being in motion. in body, in spirit, in the now. boost, it's not just nutrition. it's 26 vitamins and minerals and 10 grams of protein. it's choosing to go up. boost, be up for it. number one in just 60

tonight florida under siege from the most powerful storm the east coast has seen in over a decade. our team is on the ground in the storm zone. >> reporter: hurricane matthew, a demon in the dark. the massive category 4 storm with winds of up to 130 miles per hour is wreaking havoc on the sun shine state. a strong warning from the state's governor. >> unfortunately, this is going to kill people. >> reporter: more than 3 million people urged to clogging major highways up and down the coast for miles. preparations for matthew's arrival going on for days. gio benitez is in florida. >> reporter: were feeling the powerful wind and rain. we're in the west palm beach area. we hope to not be near the eye wall. it will be dangerous if it comes

you'll have the 100 miles per hour winds there. some 2 .5 million people are expected to be without power in florida by morning, and it will take that long to figure out where that damage is. >> reporter: so far power lines going along the coast, tens of thousands, already without power. abc is tracking the storm. >> reporter: a major concern, the storm surge. where i am along the coast of florida it's expected to be 6 to 10 feet or the waterway behind me would rise, and for residents here, flooding is a fear. >> reporter: hurricane matthew is expected to continue moving up the coast, impacting jacksonville, parts of georgia before hitting charleston, south carolina. matthew has torn a vicious path toward the caribbean, devastating haiti. the destruction there is still

baja mas today. causing widespread flooding. the impact zone on lockdown. tonight close to 4,000 flights cancelled. disney world closing down in orlando for the fourth time in history until the storm is over later friday. >> matthew remains a powerful hurricane into tomorrow as it makes its way into northern florida and georgia. we'll have more throughout the night and complete coverage on we turn now to a twisted murder plot. the case of a florida college professor gunned down by a hit man. but who hired him? after two years, authorities say they're finally unraveling the history. here's matt gutman. >> reporter: it was a sensational murder case. >> the mystery killing of a prominent law professor. >> murdered execution style. >> reporter: a mystery assassination of a law

stunning turn or flip. >> we change the plea at this point in time. >> reporter: one of the two hit men charged is now cooperating with the prosecution. >> do you understand what you're doing? >> reporter: the man who clammed up for months has now opened up, talking with prosecutors in exchange for a vastly lighter sentence. prosecutors say rivera and his accomplice were hired for the alleged hit. it was july when mark jrnelle was shot in his garage. who would want the beloved professor dead in his beautiful ex-wife also a law professor told the police not everything had been amicable in their divorce. >> it caused me a lot of grief, but i would never do something like this. >> reporter: her boyfriend at the time told police that her

for blocking wendy and their kids from moving away. >> the family desperately wants her back in south florida. mother, father, and she has a brother. >> they hate danny in a way i've never seen this kind of obsession. >> reporter: was that enough for him to take a hit out on the professor. as police dig in, they discover a toyota see rented by a member of a gang. lusi ri vera. this video showed that prius following the professor into a fitness center on the morning of the killing and trailing him on his way back home. police say that later that evening a bank security camera captured him and his police in the prius back in miami. withdrawing money from an atm.

charged with first degree murder and both pleaded not. everybody is asking who hired them. prosecutors say the plea deal this week may be the key to solving that mystery, and well worth the lighter sentence. >> i can understand why it was necessary to move forward and try to hold everyone accountable that has a part in this crime. >> reporter: she says the cooperation has led to the arrest just last weekend of this key suspect, kathryn. wendy adelson's family. she's the mother of accused hitman gars's two children, and she's also the girlfriend of wendy's brother, charlie. >> reporter: did charlie have anything to do with the murder? >> no. he's being looked at because he had a dating relationship with katherine. however, there is no evidence

none. >> reporter: but according to an arrest affidavit, they believe the murder was arranged through her and she made cash deposits of over $56,000 in the 16 months following the murder. police also say an informant told them that charlie picked up half the tab for a pricey breast job three months after the murder. police say that ri vera who was incarcerated in an charge said she had all the money and she needed to be nice to him and give him bail money. armed with that information, police set up a sting this april rattling them who were happily reunited with wendy and the two kids in south florida. >> excuse me. >> reporter: watch what happens when donna is alone. she's approached by an

rivera's brother. he presses her for payment for services renders. >> my brother helped your family. he's going through some rough times. i want to make sure he's taken care of what he's going through. >> i don't know what you're talking about. >> this will explain it. thank you. >> she has the paper. they're walking away. >> reporter: police say inside the envelope is a press release about the for $5,000. how would the grandmother react? >> hello? >> this is mrs. adelson. >> reporter: "nightline" exclusively getting this recording of her call back to that undercover agent three weeks after the sting. >> i don't know your friend who is in jail. i'm sorry your friend is in jail, but i don't know what that has to do with me. >> you know exactly what it has to do with.

i ask to send the $5,000. everybody knows what's going on. >> you're saying everyone knows. i know i lost my exson-in-law. i did not have anything to do with it. >> reporter: she sticks to her guns adamantly denying any knowledge of a plot. but police say the rus still worked. that her call followed a series of nervous conversations between theed alsons, matt, and the alleged hitman. po up the five grand but never do, and according to police documents, charlie, wendy's brother, allegedly said he wanted that mysterious messenger eliminated permanently, saying you'd better kill him because he's going to be a big problem. if you can't do it, i'll have someone else do. police had heard enough. this may they submitted arrest affidavits for charlie and katie stating they were responsible

at the time the prosecutor declined to file charges citing insufficient evidence. when abc news ought up with charlie, he wasn't eager to answer our questions. >> reporter: dr.ed alson, were you involved in a plot to kill dan markelle? did you discuss hiring a hitman. >> reporter: attorneys have said the accusation of their involvement are nothing more than fanciful fiction, and in response to the plea deal, charlie's attorney said the avoid the death penalty. but with him koormting and another in custody, prosecutors want to turn that hope of future arrests into reality. for "nightline," i'm matt gutman in florida. up next, a former cheer leader who suffered six concussions. warning young athletes and parents about what's become the most dangerous sport for young women in america. your cafe au lait?

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when you think of dangerous contact sports you probably that's what it's become. a long way from the chanting and pom pom waving to the past. modern cheer leaders are more like competitive gymnasts with a high risk of injuries. here's paula ferris. >> reporter: competitive cheering is not for the faint of heart. the flips, jumps, and tosses require physical and mental toughness. but it's the falls that make it the most dangerous sport for

a bad fall can have serious, even catastrophic consequences. just ask katelyn banky. >> it took over my life but in a good way. i think cheer really shaped who i am today. >> reporter: she started competing at six. >> it was cheer 100%. 15 hours a week for 15 years. >> reporter: over the course of 15 years she suffered five concussions, all from cheer leading. her first concussion was when she was 13, not from flying and falling but from being the base. >> i caught the girl and both my arms were around her, and i mis hit my head right on the basketball floor. that one was scary, because i did lose vision for a while. >> reporter: but she didn't stop cheering. >> i avoided going to the doctor. i tried pushing myself too hard to get back in really fast, because i didn't want to miss cheering at the next big game.

concussions, there is still a suck it up attitude in the sports culture. we need to realize that you cannot roll the dice with your brain, health and well being. >> reporter: cheer leading evolved from cheering on the sidelines to a highly competitive, international sport. and the pressure to win by doing even higher jumps and more challenging throws is intense. >> i wouldn't want to people by giving up. >> reporter: two years ago we spent time with carli manning, a competitive cheer leader in texas. like katelyn, she, too, had been training for over half her life. >> i usually have about 16 hour days. >> reporter: we followed carli and her team as they prepped for the world championships. >> practices are very important, especially here at triathletics. that's where you're trying to earn your spot. >> reporter: her ability to fly

helped the wildcats consistently beat the competition, but perfecting the routines is brutal. before a major competition, carli can train for up to 15 hours a week. that's on top of full-time school. >> when you come in here for the next practices, including if you have mono, strep, if you have a broken leg and the bone is sticking out the side of your body, you have a smile an your face practice. >> you can do it. >> reporter: but the more challenging the routine, the higher the risk. >> flipping, spinning, throwing girls in the air is a dangerous part of cheer leading. >> reporter: i broke my right ankle. i've had various hamstring injuries. >> i want to do it until my body breaks. >> reporter: competitive cheer is a short lived career. carli has become a celebrity of sorts with over 500,000

she's now 18 years old and a sophomore cheer leader at oklahoma state university. hundreds of thousands of her followers still watch her gravity defying moves. the popularity of this sport is growing, but so the are injuries. in 1980 there were nearly 5,000 emergency room visits caused by cheer leading. that number jumped to over 26,000 in 2007. in fact, second only to football in the number of direct catastrophic events among high school and college sports. >> there are a lot of myths out there, and one of them is that you have to black out or have a loss of consciousness to have a concussion. that's not true. we know that 90% of concussions occur in people who have not lost consciousness or blacked out. >> reporter: as for katelyn, she was a sophomore on the squad at the university of texas when she had concussion number four.

to see the long-term effects. >> i really started having some memory issues. short-term memory issues, not being able to remember where i parked my car, not being able to find words when i was talking. headaches. i've had a lot of issues with depression. >> reporter: she's been forced to say good-bye to her lifelong passion because the risk of continuing was too high. >> i decided i had to quit when we were talking about the fact that i have a life ahead of me, and if i continue to cheer, i would get more concussions, and who knows what the side effects of those ones would be. >> reporter: high schools and colleges have protocols in place for reporting red trauma, but katelyn hopes cheer leading will become recognized as a sport so concussions, are combatted as

smarter and sat out longer and let myself truly recover and not gotten the repetitive concussions, i wouldn't be in the position i am now. >> when we come back, more updates on hurricane matthew and the path of destruction. ? ? ? one smart choice leads to the next. ? the new 2017 ford fusion is here. it's the beauty of a well-made choice. ? with my moderate to severe crohn's disease,...

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in recapping the top story, we continue to track hurricane matthew. looming off the florida coastline. the bands wreaking havoc, heavy rains and forcing the mass evacuation of millions of people. tens of thousands have already lost power. with our team in the storm zone, we'll keep you updated throughout the night and early tomorrow on good morning america. thank you for watching abc news,

abc news and our "nightline" facebook page. good night, america. ?[music] ? they're trapped. forced to sleep in a hotel ballroom by the wrath of hurricane matthew. >> infants and toddlers. lots of babies cries. >> and look whose estate is at