"It was a fishing-type vest -- a jacket with a lot of pockets. It was not a bulletproof vest," state police spokesman Lt. J. Paul Vance told the New Haven (Conn.) Register.
ABC News and some other news organizations initially reported Lanza, 20, wore a bulletproof vest Dec. 14 when he fatally shot 20 schoolchildren and six adult staff members and wounded two at the school.
Lanza earlier shot and killed his mother, Nancy Lanza, at their Newtown home, police said.
After killing the students and staff members, Lanza committed suicide by shooting himself in the head as first responders arrived, police said.
Connecticut restricts bulletproof-vest purchases, requiring sales to be made in person. People convicted of most felonies can't buy or possess body armor.
Police asked lawmakers to adopt the 1998 legislation "because they were encountering criminals who were wearing body armor," Michael Lawlor, a state criminal justice undersecretary, told the newspaper.
A utility vest like the one Lanza wore is readily available and would not have aroused suspicion, Bridgeport, Conn., police officer Dwayne Harrison, president of the local National Association of Government Employees chapter, told the Register.
"Some kids just get those for fun," he said. "In this case, maybe he had that for magazines and bullet rounds."
The information came as a New York City woman was arrested and charged with lying to federal agents after allegedly posing as a relative of a boy killed in the mass shooting to collect donations.
Nouel Alba, 37, of the Bronx, claimed to be an aunt of 6-year-old Noah Pozner and used her Facebook account, phone calls and text messages to solicit money for a "funeral fund," a criminal complaint filed in U.S. District Court in Hartford states.
Alba denied she posted any messages on Facebook soliciting donations when asked by law enforcement about the alleged scheme, officials said.
Alba was released on $50,000 bond at her Hartford arraignment Thursday. Her public defender, Deirdre Murray, had no immediate comment.
If convicted, Alba faces a maximum of five years in prison and a $250,000 fine.