Ex mother-in-law of murdered FSU professor arrested just days after her son's conviction

MIAMI -- There has been a stunning arrest in a murder-for-hire plot that left a Florida State University law professor dead nearly a decade ago. The victim's former mother-in-law was taken into custody as police say she was trying to leave the country.

Dan Markel's former mother-in-law Donna Adelson is now facing murder charges. The 73-year-old was arrested at Miami International Airport Monday night after attempting to board a one way flight to Vietnam.

"She was apprehended on the jetway she had literally checked in and was walking into the plane," said Jack Campbell, Florida Second Judicial Circuit State Attorney.

Markel was 41 years old when he was gunned down in the driveway of his Tallahassee home in 2014 while in a bitter custody battle with his ex-wife Wendi Adelson.

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Adelson wanted to relocate their two boys to South Florida to be closer to her family but Markle refused. That's why prosecutors say the Adelson family took matters into their own hands.

Just last week, Wendi's brother, Charles Adelson was convicted for Markel's murder. The Florida dentist was also found guilty of soliciting and conspiring with three hitmen to carry it out.

Now, prosecutors say Wendi and Charlie's mother helped arrange that murder plot, too.

In this police surveillance video, an undercover FBI agent confronts Donna and demands more money after the murder. Investigators said she later made this call to her son.

According to the probable cause affidavit obtained by ABC News, Donna spoke to Charles in multiple jail calls over the past week where she told him she was getting things in order, creating trusts and making sure her grandchildren are taken care of. She even discussed plans for suicide or fleeing to a non-extradition country. Soon after, prosecutors claim she booked that one way flight to Vietnam, with a layover in Dubai.

"When we found that she was leaving the country, extradition would have been an issue and that was when the decision was made that we needed to kind of expedite," Campbell said.

Donna appeared before a Miami judge Wednesday morning and is being held without bond.

The Markel family did not comment on her arrest but told ABC News in September how relieved they were after Charles was arrested.

"It has taken so long, we want the people involved to pay the price," said Dan's father, Phil Markel.

Both Donna and her daughter Wendi -- Markel's ex -- have previously denied any involvement in the crime. Wendi has never been charged.