WASHINGTON — The Justice Department moved Thursday to fix what it described as “an information gap” that has allowed offenders living on Native American reservations to buy guns illegally and for years has blocked tribal police from access to important criminal records.

The flaws in the system were on stark display last year after a 14-year-old boy from a reservation in Washington State used his father’s handgun to kill four classmates and himself. Investigators determined that a prior restraining order against the father should have prohibited him from buying the gun, but the order was never entered in the federal database.

In an announcement timed with the Tribal Nations Conference at the White House on Thursday, the Justice Department named 10 Native American tribes around the country to share criminal and civil records with the federal government through a trial program expected to cost about $1 million. Officials hope to expand the program to other tribes.

With crime a longstanding problem on reservations, tribal police have complained for years about spotty access to important legal databases run by federal and state governments. They say the problem has hindered not only the ability to identify illegal gun purchases, but also to apprehend fugitives, investigate crimes and guard against domestic and sexual assaults.