The drunken driver who decapitated 7-year-old flower girl Katie Flynn and also killed her family’s hired chauffeur after a Long Island wedding has been released from prison — sparking outrage from the victims’ kin.

Martin Heidgen, 43, who served 19 years behind bars for second-degree murder in the July 2, 2005, wrong-way horror on the Meadowbrook Parkway in Freeport, walked out of prison Wednesday after being granted parole, the state Department of Correction and Community Supervision confirmed Sunday.

For the families of little Katie and slain limo driver Stanley Rabinowitz, the system failed.

“This liberalism is a bullet into the back of the families who suffer the loss of their loved ones,” Joyce Rabinowitz-Schuster. the driver’s widow, said in an email to The Post.

“There is no accountability in New York State anymore. Murder should be 25 years minimum. Crime is rising in NYS because of these dismissive attitudes and it must stop,” she wrote.

“My family and the Flynns and Tangney families [Katie’s maternal grandparents] realize this crime every day and the hundreds of other friends and family members of the victims involved in this murder,” Rabinowitz Schuster said. “Shame on the parole board who released a murderer.”

Heidgen, who was 24 at the time of the fatal wreck, had driven his pickup truck the wrong way for nearly 3 miles when he slammed head-on into the limo as it returned from an idyllic beach-front family wedding in Bayville.

His blood-alcohol content was more than three times the legal limit when he crashed, authorities said.

In the limousine were Katie, her little sister, Grace, 5, their parents, Neil and Jennifer Flynn, and Jennifer’s parents, Denise and Chris Tangney, a retired Nassau County cop.

The wedding was for Jennifer’s sister.

In a statement to Newsday, which first reported Heidgen‘s release, Katie’s parents said the parole board’s decision to release their young daughter’s killer has had a “profound impact” on the family.

“We asked that the public may know our sadness and feel our pain,” Jennifer Flynn told the outlet. “Katie was murdered as a 7-year-old girl; where her murderer lives, imprisoned or paroled, makes no difference in our lives.

“We realize that our news cycle is over, but it is our hope that your readers think of us and that we influence their choices.” 

Heidgen was sentenced to 19 years to life after being convicted on two counts of murder, three counts of first-degree assault and tampering with physical evidence, state officials said.

The convict tried to appeal the verdict after being imprisoned but was shot down.

A spokesman for the state DOCCS said Sunday that a parole board granted Heidgen conditional release Aug. 13 and that he was cut loose Wednesday.

The terms of his release include remaining in the state unless given permission to leave.

Heidgen’s lawyer did not immediately respond to a request for comment from The Post but in a statement to Newsday said that his client remained haunted by the tragedy.

“Both Marty and his family are grateful to the parole board of recognizing that it is appropriate for Marty to be released on parole and allow him to reenter society and become a productive and constructive member of our community,” the lawyer, Stephen LaMagna, told the outlet.

“He is and remains forever remorseful for all of the pain he has caused to so many and continues to pray for them and their families,” LaMagna said in the statement.