(CNN) -- A missing University of Florida student's backpack was found at the residence of a suspect, whose car tested positive for blood, Gainesville police said Saturday.
The developments came as authorities continued searching for Christian Aguilar, 18, last seen September 20.
At a court hearing Saturday, a judge denied bail for Pedro Bravo, 18, charged with first-degree murder in Aguilar's apparent death.
Aguilar's backpack was found hidden inside a suitcase in Bravo's closet, police spokesman Officer Ben Tobias said in a statement explaining what led authorities to charge Bravo with murder.
Blood found in several locations in Bravo's vehicle will undergo an expedited analysis and be compared against known DNA samples of Aguilar, Tobias said.
Bravo changed his account of what happened "after being confronted with evidence that disputed his initial statements," Tobias said Saturday.
Bravo had told investigators he got into "an altercation with Aguilar" the night the college student went missing, police said.
The suspect then left Aguilar in a parking lot in the central Florida city, prompting police to warn that Aguilar may be disoriented and/or seriously injured.
Aguilar's father told CNN affiliate WCJB that his son disappeared after a fight over a girl.
After talking with police a day after his disappearance, Bravo was held for mental examination after threatening to harm or kill himself. He was later charged with depriving a victim of medical care, a third-degree felony, and was in custody at the time he was charged with murder, according to Tobias.
Scientists have confirmed lime rock residue was found on Bravo's vehicle, police said Saturday. "We believe that Christian Aguilar may be located near areas of lime rock," Tobias said.
The police spokesman previously said, "we would ... encourage property owners, residential or business, who may have lime rock roads on their property, that were accessible to the general public, to search those properties for any suspicious areas of ground that appear to have been disturbed," Tobias said.
"We are also requesting information from anyone who may have seen a suspicious vehicle, likened to a Blue Chevy Blazer, in any remote areas on the night of Thursday, September 20."
Authorities have used helicopters and K-9 units to search for Aguilar, to no avail. His relatives have plastered the area with fliers, taken to Twitter to generate leads and invited a nonprofit search group to help look for him alongside family members and police.
Bravo's lawyer said his family initially volunteered to help in the search, only to be politely turned down by the victim's relatives.
Gov. Rick Scott was to join the search Saturday in a wooded area in Gainesville, his office said.
CNN's Joe Sutton and Greg Botelho contributed to this report.