Officer William Porter, charged with manslaughter, has said he did not call for a medic for Freddie Gray because he had no reason to do so.
A prosecutor said Mr Porter could have easily called for a medic or used a seatbelt in the back of a police van.
Gray died a week after sustaining a spinal cord injury in the van.
His death sparked protests over police brutality, with the city of Baltimore erupting in rioting, looting and arson on the day of his funeral.
Prosecutor Janice Bledsoe said during closing arguments that Mr Porter "just didn't care enough" to secure Gray with a seatbelt or call for medical attention.
Mr Porter said he checked on Gray during the stops, and he had no signs of injury.
He is charged with manslaughter, assault, misconduct in office and reckless endangerment and could receive up to 25 years in prison.
Other officers' saying they do not use seat belts on prisoners is not an excuse, she said.
Mr Porter said Gray asked for help getting off of the floor of the van and denied claims that Gray told him he could not breathe.
However Mr Porter did say he hear Gray say something about needing an inhaler upon his arrest.
He said in 200 arrests involving the van, he has never belted a prisoner because the wagon is "pretty tight".
"External facts" show Mr Porter is telling the truth, his lawyer Joseph Murtha said, according to the Baltimore Sun.
Mr Murtha said Gray's death was a "horrible tragedy" but that there is no evidence Mr Porter is responsible for it.
Concerned about possible unrest after the verdict, Baltimore is opening an emergency operations centre as the trial wraps up.
Mayor Stephanie Rawlings-Blake has said she is sure city officials are prepared for any protests that may arise.
Five other Baltimore police officers will go on trial in Gray's death. All have pleaded not guilty. They will be tried separately and prosecutors hope to use Mr Porter as a witness in the other trials.

The country has also been subject to economic sanctions by the West over its involvement in the crisis in Ukraine.
Russia will spend most of the cash on federal loans, pensions and recapitalising its banks.
The country will also make public spending cuts.
Over the next three years most spending, apart military and social programmes, will be hit.
Earlier this month, the International Monetary Fund forecast that Russia's economy will contract by 3% this year and 1% in 2016.
Russia's government will spend about one trillion roubles to recapitalise banks through the issue of government bonds.
The plan includes a separate scheme to help recapitalise some banks with 250bn roubles, while 300bn roubles will be provided to Vnesheconombank, the state development bank.
There will be an extra 200bn roubles in state guarantees to finance investment projects, and regional governments will get 160bn roubles in federal loans.
Meanwhile, the government has proposed public spending cuts of 10% this year and 5% over the next two years.
The cuts have yet to be approved by the Russian parliament.
A Baltimore officer on trial over a death in custody has been accused of turning a police van into a coffin on wheels, prosecutors have argued.
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The Russian government is to spend at least 2.34 trillion roubles ($35bn, Â£23bn) to try to stave off an economic crisis, following a collapse in oil prices and the value of the rouble.