Officers told Channel 2's Tom Jones the information is preliminary at this point.
"Keep in mind this is just coming from a neighbor that's saying he thinks it may be coming from somebody that goes to this particular high school," police Maj. Johnny Robinson said.
Robinson said the tipster told them he may know the gunman.
On Monday, a neighbor said he spotted the gunman in his neighbor's backyard with the rifle.
He said the man pointed at an approaching school bus as children boarded.
The neighbor said he yelled at the gunman and that's when he took off and got away, leaving the rifle, ammunition and a note.
Robinson said the note had information that may point to the gunman's intentions.
"It did have some numbers on there and it does look like it's going to be some bus numbers," he said.
Robinson could not say if the bus numbers matched the number on the bus the children were boarding.
Robinson also said officers did not find any fingerprints on the rifle, the ammunition or the note.
Officers did locate the name of the person who the rifle was originally registered to. They said it was purchased in 1985. They're still trying to locate that person in hopes they can help explain how it ended up in the hands of the gunman.
"Maybe he or she can or will be able to tell us what they actually did with the weapon. If they sold or traded it or anything of that nature," Robinson said.
Officers said the weapon wasn't reported stolen and they said the original owner doesn't fit the description of the gunman.
Meanwhile, parents said they are too afraid to allow their children to ride the bus, so they are picking them up and dropping them off at school.
Shay Simmons said she's not taking any chances.
"Cause I don't know. They didn't catch him yet," she said.
Police continue to escort buses to and from school to make sure children are safe.