"Right now, there are more questions than we have answers", the chief said.
While inside, she pulled her firearm and shot Jean.
Authorities did not provide further details about how the altercation unfolded, but the officer eventually fired her gun and hit Jean.
Police have not released the name or race of the officer, who arrived home in uniform and was not injured.
A Dallas police officer is on leave after she entered an apartment "believing that it was her own", and fatally shot a man inside, according to police.
The responding officers administered first aid to Jean, a native of the Caribbean country of St. Lucia who attended college in Arkansas and worked for accounting and consulting firm PwC. Jean, who was black, was taken to a hospital and pronounced dead.
Police have not spoken to any other individuals at this time and did not say that there were any witnesses. When the circumstances "led us to another direction", she said the department invited the Texas Rangers to take over and conduct and independent investigation.
After graduating in 2016, Jean began a risk assurance internship at PricewaterhouseCoopers.
Botham's employer, PricewaterhouseCoopers, issued the following statement: "This is a bad tragedy".
Family and friends described Jean as a devout Christian and a talented singer. "Gone with the Angel's. lord keep me sane", Jean said.
"How can you make a mistake like that, getting into someone else's apartment?" an 80-year-old woman who identified herself only as Raquel said. Alongside photos of the young man grinning in a suit and hanging out with his family, clinking glasses in a kitchen, Earl said it was the worst day of his life.
"Originally from St. Lucia, Botham was a member of Good News Singers, a resident assistant, an intern for the Rock House campus ministry, and a leader in Sub T-16 men's social club", Harding University said in the statement.
Fullinwider, 66, who has been an activist in Dallas for decades, said he hopes Oliver's conviction signals that Americans want to stop letting officers who kill civilians get away with murder.
Star-Telegram media partner WFAA reported that the apartments are just two blocks from police headquarters.
Neighbours said they can access their building with a regular key or by using a keypad code.