Insets: Sue Ann Marcum and Jorge Rueda Landeros. Background: The home in Bethesda, Maryland, where Landeros killed Marcum (Montgomery County State Attorney's Office).

A 56-year-old man is headed to prison for decades, more than 15 years after he murdered a popular college professor in Maryland, fled the country and assumed a new identity.

Jorge Rueda Landeros was sentenced on Tuesday to 25 years behind bars for the slaying of 52-year-old Sue Ann Marcum, according to the Montgomery County State Attorney's Office. A jury found Landeros guilty of second-degree murder in October.

Landeros was Marcum's Spanish teacher and yoga instructor and the two had become lovers. Marcum, a beloved professor at American University, also entered into an investment deal with Landeros. But Marcum soured on the deal.

"The vision of you sitting at the end of my kitchen table telling me you have no remorse for spending the money keeps appearing in my head now that I know that the amount was $50,000; it is physically playing havoc with my body," she wrote in an October 2008 e-mail to Landeros.

Investigators later learned that Marcum forked over some $300,000 without getting anything in return. Landeros pocketed about $250,000 of the money. He also made himself the sole beneficiary of Marcum's $500,000 life insurance policy.

Cops found Marcum dead on Oct. 25, 2010, inside her home in the 6200 block of Massachusetts Avenue in Bethesda. She had been strangled and beaten. It appeared someone had gained entry through a rear window and some items of value were stolen. However, over the course of the investigation, cops determined that the burglary was staged and Marcum likely knew her killer.

Detectives recovered DNA belonging to someone other than Marcum. They then reviewed Marcum's emails, which uncovered her relationship with Landeros. They also learned he had crossed the U.S. border from his native Mexico just days before the murder. Landeros had been going back and forth from the U.S. and Mexico on a regular basis and during one of the crossings, Border Patrol agents obtained a cheek swab for a DNA sample.

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In April 2011, authorities confirmed the unknown DNA at the crime scene belonged to Landeros. They obtained an arrest warrant.

But by that time Landeros disappeared into Mexico. Cops learned that he assumed a new identity. It took 11 years before authorities could locate him, arrest him, and ship him back to Maryland to face charges.

A jury convicted him of murder after a nine-day trial.

Marcum's brother Alan Marcum noted that Monday was his sister's birthday.

"Today, we're standing here with the person who murdered her sentenced to 25 years thanks to the work of the Montgomery County police, the State's Attorneys, and I'm very grateful for the work that they did, and appreciative for the care and attention that the jury paid and that the judge gave us throughout this case," he said.

Sue Ann Marcum was the director of the master's in accounting program at American University and taught both graduate and undergraduate classes, her obituary said. She was professor of the year for three straight years.

Her longtime friend Larry March said Marcum had recently moved into a new home, and he believed she had cut all ties to Landeros.

"She was kind of starting her life over again, and then she was snuffed away from the Earth," March said.