A man who had been on the run from the FBI for almost 50 years after escaping police during his grandmother's funeral has been re-arrested, authorities said Friday.

Leonard Moses had been jailed for life for throwing Molotov cocktails together with a group of others during riots that followed the assassination of Martin Luther King Jr in 1968. The petrol bombs set fire to the Pittsburgh house of Mary Amplo, who was severely burned and later died as a result of her injuries.

In 1971, Moses was granted a furlough to attend the funeral of his grandmother and used the occasion to give police the slip, changing his name to Paul Dickson and working, at least since 1999, as a travelling pharmacist in the state of Michigan, police said. 

The FBI renewed their search in 2016, questioning his family once again and offering a reward for his arrest, as well as setting up a dedicated tip hotline.

Despite more than 2,000 tip-offs, the FBI were "still unable to locate and apprehend Leonard Moses," said FBI agent Michael Christman, an FBI official at a press conference in Pittsburgh.

But at the beginning of this year, he was detained and questioned in the course of a separate investigation, whose nature the FBI did not disclose.

Legal records show that a Paul Dickson, born in 1949, was arrested in the state in April for fraud and writing illegal prescriptions for controlled substances.

In the course of the investigation, the suspect's fingerprints were taken and fed into a law enforcement database, eventually proving a match for the federal records the FBI held on Moses.

He was arrested Thursday without incident at his home in Grand Blanc, Michigan, and was due to be transferred to Pennsylvania.

"I hope this arrest brings some closure to the family members of Mary Amplo, who was killed back in 1968," said Christman.