"There's a lot of evidence that we look at," said Hawaii County Prosecutor Mitch Roth. "We sent evidence to different sources to make sure that the vehicles were operating in order."
The man who died, Jeffrey Surnow, 63, of West Bloomfield, Mich., was known a a strong and experienced bicyclist who competed in the Ironman and organized cycling events in his hometown.
Investigators said Buddemeyer struck Surnow from behind as he was riding his bike eastbound on Waikoloa Road.
Roth said it's not unusual for fatal accidents to take so long to produce to charges.
"There's other information that we're doing, that we had experts looking at the evidence and sometimes they take a while to get back," said Roth.
Buddemeyer was a Honolulu police officer before joining the Hawaii County police department. He was relieved of his duties in May 2015, two months after the crash.
Since that time, the cycling community got the county to add a shoulder on that stretch of highway.
"A big, nine-foot shoulder, top to bottom of Waikoloa Village Road, and we're extremely grateful for the attention that's been given, not just for the cyclists, but for all road users," said Rich Bell of Bikeworks Beach and Sport, a Waikoloa bike shop.
Meanwhile, bicyclists in the area are reminded of Surnow: a so-called "ghost bike" marks the spot where he died.
"We ride by his ghost bike almost every day," said Bell. "And it's very emotional because I feel for his family and also feel for the family of the officer."