BOSTON (AP) – Federal prosecutors are asking a judge to block the imminent release of a career criminal who has allegedly stalked numerous female employees at the federal prisons where he’s been held for the last 18 years.

John Leonard Ecker already had a long criminal record that included convictions for arson, armed assault, breaking and entering and burglary when he was indicted on a federal charge of being a felon in possession of a firearm in 1989.

He was committed to federal custody for hospitalization after federal officials found that he was mentally ill, incompetent to stand trial and dangerous to the public.

Ecker, now 47, spent the next 18 years in various prison hospitals, where, prosecutors claim, he developed “romantic fixations” and stalked female employees of the U.S. Bureau of Prisons.

But in March 2006, a federal judge dismissed his 1989 indictment because he had been committed for 16 years – longer than the 15-year prison term he would have faced if he had been convicted.

Since the criminal indictment was dismissed, Ecker has remained at the Federal Medical Center in Springfield, Mo., because of his mental health problems.

Now, Ecker, who grew up in Wilbraham, wants to come back to Massachusetts so he can be near family members in Massachusetts, according to court filings.

Ecker’s lawyers have asked U.S. District Judge Nathaniel Gorton to transfer him from the federal facility in Missouri to a state facility in Massachusetts. Authorities from the Massachusetts Department of Mental Health have repeatedly rejected requests to take Ecker, saying they have no place secure enough to house Ecker, who has been diagnosed with paranoid schizophrenia and anti-social personality disorder.

In a contentious court hearing Tuesday, Assistant U.S. Attorney Mary Elizabeth Carmody did not say how many women Ecker is accused of stalking or give details of his actions, but said, “The women who have been victims of this stalking are terrified.”

Federal prosecutors argued that Ecker should remain in federal custody for at least 12 to 18 months while authorities determine whether he can be released without creating a risk to the public.

Carmody said prosecutors have “grave concerns” that Ecker remains dangerous, particularly to women he has stalked while in prison. She said Ecker has a history of not taking his medication, which causes him to become “psychotic and violent.”

“If he doesn’t take his medication, he is dangerous,” she said.

Following the hearing Tuesday, Gorton gave the warden at the Missouri prison 60 days to submit a plan for Ecker’s release to a less restrictive environment, which could include a halfway house or group home where he would be monitored by the U.S. Bureau of Prisons. After six months of such a “conditional release,” Ecker could be released if authorities determine he doesn’t pose a danger.

Massachusetts officials would still have the option of attempting to have Ecker civilly committed in state.

During Tuesday’s hearing, Groton cited a letter in which the warden in Missouri said clinicians there have concluded Ecker is no longer in need of inpatient treatment and would not pose a serious risk of danger to others if he is released.

“Why should I not interpret that letter as a certification that Mr. Ecker is ready for conditional release?” Gorton asked Carmody.

Neil Smith, one of Ecker’s attorneys, said Ecker should be released.

“He’s already been in prison for 19 years. It’s time to give him a chance to get out,” he said.