ALBANY, N.Y. » A man charged with killing a woman and raping her 10-year-old daughter after a carjacking at an upstate New York mall last week was able to remove and reassemble his court-ordered electronic monitoring bracelet to go undetected for hours while carrying out the attacks, federal authorities said.

David Renz, 29, put the ankle bracelet back together so quickly that it may have prompted what appeared to be a false alarm Thursday night. Officials had told the company not to notify them of the briefest interruptions of monitor signals because they were getting alerts when the bracelets simply struck something.

"He disassembled the bracelet and took it off his leg and reassembled it in a very short time frame so we were never alerted that the bracelet was tampered with," said Matthew Brown, U.S. chief probation officer for the Northern District of New York. "We’ve never had a case where someone was able to defeat the system like this."

The bracelets have light circuits that set off an alarm when disrupted, but officers had found themselves answering tamper alerts when a monitor simply got bumped. "We put in place a system where it’s got to be longer than an instant. It’s a matter of minutes," Brown said, declining to say how exactly long.

Renz was facing federal charges of possessing child pornography. A note in the case file from Jan. 11 said federal prosecutors "have changed their position in regards to detention" and agreed to Renz’s release on the recommended conditions, which included a curfew, remaining at an authorized address — his mother’s house — avoiding children and places they congregate and restricted computer use. A federal judge agreed to the release conditions.

"Ankle bracelets don’t protect people. They monitor people," said Will Marling, executive director of the National Organization for Victim Assistance. He said pretrial safety is an important issue, and he wonders what safety assessment was done on Renz.

Brown said most sex offenders, probably 95 percent, get to sentencing with no further criminal violations. "You don’t see what this guy did. It’s a complete anomaly," he said.

Defense attorneys said anyone can cut off ankle bracelets, which are usually authorized by judges for defendants accused of nonviolent crimes like drug offenses. They are advocated by authorities as far less expensive than jail and by defense lawyers as a fairer alternative for people still presumed innocent. However, longtime lawyers, authorities and contractors all said few defendants remove them, since it usually means going right to jail and facing an additional criminal charge.

"I did have a client cut one off one time. He was caught almost instantaneously," said Albany attorney Terence Kindlon. "If nothing else, it’s considered an insult to the authority of the court."

An alarm generates a phone call to the defendant, followed by calls to family, friends and collateral contacts if needed to find him. If that fails, and the defendant is deemed dangerous enough, Brown said they’d go to a judge for an emergency warrant, then try to find the person.

Police said Renz went to the mall in suburban Syracuse and abducted the woman and her daughter as they left gymnastics class. He bound them, raped the girl and stabbed the woman, authorities said. The girl escaped.

In Renz’s case, Brown said the Boulder, Colo.-based contractor, BI Inc., notified them about 4 1/2 hours later, about 11:30 p.m. Thursday, with an alert that the bracelet, operating with a global positioning system, wasn’t moving.

Company spokeswoman Monica Hook declined to discuss what happened.

Renz, now in isolation after he was beaten by another prisoner in the Onondaga County jail, is charged with murder, rape and kidnapping.