Marijuana is to blame for much of the city's spike in homicides and shootings during the beginning of this year, causing the NYPD to examine a few select precincts as largely responsible for the increases, Police Commissioner Bill Bratton said Monday.

There were 54 homicides for the first two months of the year, a 20% increase from the same time last year, according to NYPD statistics. More than 70% of homicides were the result of a shooting.

And many of these homicides, NYPD officials said, were marijuana-related "rip-offs."

"It's ironic in some respects, the city that is kind of the transfer point for huge amounts of drugs ... huge seizures of heroin, cocaine, hallucinogen, that the one drug that is actually the causal factor in so much of our shootings and murders is marijuana," Bratton said during a news conference at police headquarters. "The seemingly innocent drug that is being legalized around the country, in this city people are killing each other over marijuana more so than anything having to do with what we dealt with in the '80s and '90s with heroin and cocaine."

Overall crime is down about 11% this year, compared to the same time period last year, said Dermot Shea, the NYPD's deputy commissioner of operations. And there were about 6,500 total major crimes last month, the lowest for February on record going back to 1993, according to NYPD statistics.

A large percentage of people who have been arrested for homicide this year have a prior arrest history, Shea said. Of those, there are twice as many with a history of marijuana arrests than any other controlled substance.

Shea said arrests for marijuana possession, however, are significantly down: there were 80% fewer arrests in January and February of this year than the same time in 2011.In November, Bratton said New Yorkers, under many circumstances, caught with small amounts of marijuana in open view, 25 grams or less, will be issued a summons instead of arrested.

Bratton reiterated his belief that the slowdown of stop and frisk does not have anything to do with the increase in homicides.

Most of the shootings in 2015 have been focused in a handful of precincts, including Morris Heights in the Bronx, East Flatbush, Flatlands and East New York in Brooklyn, as well as Kew Gardens, and Richmond Hill in Queens, said Chief of Department James O'Neill.

"This is not the bad old days roaring back," Bratton said, adding that it is not a "precursor of worst to come. Our sense is that we have a pretty big handle on it at the moment."

The marijuana-related homicides are "rip-offs, not turf wars," said Chief of Detectives Robert Boyce.

In December 2011, Officer Peter Figoski was shot and killed while responding to a drug rip-off, he said. Five men were charged with killing the veteran officer after they tried to rob a marijuana dealer in Cypress Hills.