Aguilar fired six to eight shots during the rampage at the Columbia mall yesterday, killing two employees - a man and a woman - of a skateboard shop.
The motive behind the shooting, which left five others injured, is not yet clear.
"We have not been able to verify any type of relationship between him and either of his victims...That is an open question," Howard County Police Chief William J McMahon told reporters today. "We just don't know that and we're working to find that out now."
The centre, about 45 minutes outside Washington DC, is a popular weekend shopping destination.
The two dead reported were identified as Brianna Benlolo, 21, and Tyler Johnson, 25.