(CNN) -- A journal written by the 19-year-old gunman in last week's Maryland mall shooting offers no clues to a key question investigators are asking -- whether Darion Aguilar knew the young man and woman he shot and killed before turning the gun on himself.
While police in Howard County, Maryland, are not yet releasing the contents of the journal, they said Tuesday that from his writings, it appears Aguilar knew he had mental health issues. They did not elaborate on that point.
But why did he go to The Mall in Columbia on Saturday and fire as many as nine shots into a skateboard apparel shop?
Aguilar was an avid skateboarder, a friend of his family said. As of now, that's the only known link between him and the skate shop Zumiez.
Investigators are distributing fliers with Aguilar's picture to those in and around the mall, in hopes of finding people who either knew him or saw him.
Aguilar was known to frequent the mall, according to police, where "he would hang outside and smoke in small groups."
Investigators are also working on retrieving data from Aguilar's computer and cell phone, according to police.
Still, his motive remains a mystery.
Aguilar's mother told reporters Sunday that her son was a "gentle, sweet kid," and that she doesn't think he knew his victims -- 21-year-old Brianna Benlolo and 25-year-old Tyler Johnson.
On Saturday, a federal official briefed on the shooting told CNN that preliminary information suggested the gunman aimed only at Benlolo and Johnson, perhaps indicating it was an isolated situation and not a wider shooting spree.
"I know there's a lot of interest in the motive for this, and I have as much interest in that as anybody," Howard County Police Chief Bill McMahon said Sunday.
Benlolo was an assistant manager at Zumiez. She had worked there since November 2012, according to her Facebook page.
Friend Evelyn McDonald said Benlolo, the mother of a small boy, was "just full of energy."
"She was so nice and just an amazing artist and just an amazing person inside and out," McDonald told CNN.
"She loved her son. She loved being a mother," McDonald said.
Johnson had worked at the store for about three months, according to his Facebook page.
Five people went to the hospital for treatment after the shooting. All were treated and released.
Four suffered injuries in the chaos after the shooting. The other injured victim suffered a gunshot wound to the foot. Police said the woman wasn't in Zumiez; rather, she was on the first floor when she was hit.
The mall reopened Monday afternoon, but the Zumiez store will be closed indefinitely, according to a sign on the boarded-up storefront.
CNN's Janet DiGiacomo and Steve Almasy contributed to this report.