CNN  — 

For a year and a half, Alex Murdaugh denied he was anywhere near where his wife, Maggie, and 22-year-old son, Paul, were brutally killed.

But it was one of his victims – his son – who would provide key proof after his death that legal experts say exposed his father’s web of lies and ultimately led to his conviction in the double homicide.

“It is ironic, in the end, that it was the victim, Paul Murdaugh, who solved his own murder,” Dave Aronberg, state attorney for Florida’s Palm Beach County, told CNN Thursday night.

Murdaugh, a now disgraced former South Carolina attorney, was found guilty Thursday of fatally shooting his wife and son and, a day later, was sentenced to life in prison without the possibility of parole. He has maintained his innocence.

The key proof came from a video, which Paul recorded moments before he was gunned down and killed. It appeared to show one of the family’s dogs near the kennels on their property. It also captured Alex Murdaugh’s voice in the background – and placed him at the scene of the crime.

The video, which Murdaugh didn’t know existed before the trial, marked the crumbling of his alibi and left him no choice but to take the stand and explain why he lied multiple times to authorities about his whereabouts, legal experts told CNN.

Murdaugh, while denying he killed his wife and son, testified he lied about where he was because of paranoid thoughts stemming from his yearslong drug addiction to opioid painkillers, as well as his distrust of investigators. While on the stand, he also confessed to more lies, admitting in court he had stolen millions from his law firm and clients over roughly two decades.

He told the jury that despite his repeated past deceptions, he was honest about one thing: he did not kill his family.

But jurors did not believe him.

And in a case with little to no direct evidence linking Murdaugh to the scene, South Carolina’s top prosecutor credited the video clip for the quick conviction by the jury.

“This was a circumstantial evidence case but what people have to understand is that circumstantial evidence is just as powerful as direct evidence,” South Carolina Attorney General Alan Wilson, who was part of the prosecuting team, said Friday. “I think the kennel video hung him.”

“The jury saw how he was trying to manipulate them, saw how he was lying and they read through it, and they heard the kennel video and they made the right decision.”