NEWTOWN, Conn. – Adam Lanza, the suspect in the suburban Connecticut elementary school shooting rampage, tried to purchase a “long gun” rifle from a local shop but was turned away because he did not want to wait for the required 14-day background check, law enforcement sources said Saturday.

As the western Connecticut town of Newtown continued to seek a way of coping with the grief from Friday’s shooting that left 28 people dead, including the gunman and his mother, officials pressed their search into how and why one of the worst massacres in U.S. history took place.

Sources said Lanza entered the gun store “earlier in the week” in the Newtown area and inquired about buying one rifle. He was only 20 years old, and did not have a permit for firearms, and was told about a 14-day background check that would have to be done, the sources said.

“He didn’t want to wait the 14 days,” said one source, declining to be identified because the case is still under review. “So they denied him. The sale did not take place.”

When Adam Lanza left the house, he took a Bushmaster .223 rifle and two handguns – a Glock 9-millimeter and a Sig Sauer semiautomatic, law enforcement sources said.

His divorced parents also owned three other “single-action rifles,” but it remained unclear how much access Adam Lanza had to those firearms and whether it was his mother or father who possessed the weapons, the sources said.

Authorities, meanwhile, are still putting together a comprehensive trace on all the weapons.

“We know the manufacturers, and are pretty sure when they were purchased,” a source said. “But the trace is not complete yet.”