Documents unsealed in a Vermont US District Court on 10 May identified Nathan Carman, 28, as the main suspect in the 2016 death of his mother Linda Carman.
The 54-year-old who died on a fishing trip off the coast of New England with her son when their boat allegedly sank. He was rescued floating adrift, and her body and the boat remain missing.
Court documents unsealed earlier this month in the Vermont US District Court revealed charges on eight counts against Mr Carman, including for murder and fraud in the death of his mother.
While no new evidence appeared in those filings, according to the Associated Press, legal experts and law enforcement attached to the case have expressed their opinions on the six year delay.
“It’s very difficult to charge murder federally,” said Jessica Brown, a former state and federal public defender at Vermont Law School. “So I think what the government has been doing for the last six years is to build its case to charge him with mail fraud and wire fraud”.
Law enforcement officials previously tied to the case told the Associated Press that new evidence could have been behind the federal indictment, and that prosecutors in Vermont might have been able to find different evidence to those in Connecticut, where Mr Carman is fighting for a share of his mother’s $7m inheritance.
He was also accused by the Vermont US District Court of fatally shooting his millionaire grandfather, John Chakalos, in 2013 in Connecticut, but does not charge him with that killing
“One of the issues is jurisdiction, especially when you cross state lines, and who has the ability to bring all that together under one roof,” said Donald Melanson, police chief in Windsor, Connecticut, where Mr Chakalos was killed.
“And I think that’s why, rightfully so, the US attorney’s office took that and took responsibility for that and brought everything together.” He has pleaded not guilty to both accusations and remains behind bars.
Mr Carman pleaded not guilty to the murder charges and faces mandatory life in prison if convicted of murder, CNN reported.
Additional reporting by the Associated Press.