Now the questions start piling up - beyond the unanswerable one about why promising young adults were brutally killed for what may have been the flimsiest of reasons, robbery. Two people are charged with killing Eve Carson, student body president at UNC-Chapel Hill, and one of them also in the slaying of Duke University graduate student Abhijit Mahato. Both suspects have criminal records. Both were on probation at the time of Carson's death.

At least one of the suspects apparently was scarcely monitored by the probation office. The outrageous lapses leave the public understandably frustrated with the legal system, and fearful that other dangerous criminals roam the streets because of a slack system.

Across two tense days last week, police arrested Demario James Atwater, 21, in Carson's death and Laurence Lovette, 17, in the death of both students. Within hours, The News & Observer reported that in 2005, Atwater had been charged with a felony and a misdemeanor in Wake County, and given probation. In June 2007, he pleaded guilty in Granville County to possession of a weapon by a felon. He was given probation again, an inexcusably lenient sentence in view of the theat of gun crimes.

Actually, the weapons charge was serious enough for the courts to have revoked the first probation. Yet steps by the probation office and the courts to do so weren't begun until November 2007. And still, District Attorney Colon Willoughby on Thursday told The N&O that Wake County court computers didn't show the November action.

Atwater finally was served with a violation warrant and arrested last month, when he came to the probation office. But he was quickly freed on $10,000 bond, an amazingly inappropriate amount in view of a weapons charge. Probation office records indicate a hearing on the probation violation was set for early this month. When Atwater arrived for court, the case mistakenly had been assigned to district rather than superior court, so it was rescheduled. That was on a Monday. Carson was shot to death two days later.

Commendably, just hours after The N&O reported Atwater's status as a probationer, Robert Lee Guy, director of the state Division of Community Corrections, ordered an investigation into the probation office's handling of the case.

That probe needs to be exhaustive. Getting to the bottom of the matter could go a long way toward preventing something similar from happening again. How often was Atwater supposed to visit his probation officer? If he didn't show up for appointments, were the courts asked to determine if his probation -- a privilege, not a right -- should be revoked? If not, was it because of understaffing? Weak policies? Slack personnel performance?

Lovette's rap sheet isn't extensive, but he is just 17: Any juvenile brushes with the law would be sealed. Given that another person was charged earlier with Mahato's January death, have Durham police suspected all along that Lovette was involved as well? And was Lovette following the terms of his probation?

Maybe these cases are isolated, but forgive our sinking feeling that they are not. Guy's investigation hopefully will shed light on the questions, and offer lessons to court agencies. What it won't do is lessen the tragedy, even if better supervision and timely action might have prevented two deaths.