The Chinese doctor, who killed Indian-American Yale physician Vajinder Toor last month, has been ordered by a US court to give his DNA sample to authorities investigating the case.
Lishan Wang appeared in a court in New Haven, Connecticut on May 11 but did not enter any plea.
Judge Roland Fasano granted the prosecution's motion for "non-testimonial evidence" to retrieve saliva samples from Wang.
Wang's defence attorneys did not object to the motion and Fasano told him that law enforcement officials are not permitted to question him while taking the samples so he has the right to remain silent at that time, the Yale Daily News reported.
No decision has yet been made on a probable cause hearing, which will decide whether there is enough evidence to proceed to a full trial.
Currently, the discovery process is on under which the prosecution is collecting evidence in the case.
A ruling on whether Wang would have a probable cause hearing would be made at his next court appearance on June 15.
Dressed in a large green prison jumpsuit and handcuffed, Wang remained silent throughout the May 11 hearing and stood with his head bowed.
Detained on a two million dollar bond, he has been provided a Mandarin interpreter by the court.
Wang shot and killed Toor, a postdoctoral clinical fellow at the School of Medicine and Yale-New Haven Hospital, outside the latter's Branford home on April 26.
He had also fired at Toor's pregnant wife Parneeta Sidhu, but she escaped unhurt.
According to a police report, Wang admitted being at the crime scene and said he was "sorry" for what had happened.
Toor, who had completed his medical studies in India, was laid to rest in New Haven on May 3. A private memorial service was held for him.
Toor's obituary described him as a "wonderful son, brother, husband, father and friend.
He was highly regarded by his patients who referred to him more as a friend since he would spend as long as needed by his patients".
It said he was a very loving father to his son and was "ecstatic" about the arrival of a new baby girl.
"He used to say that life was perfect. His untimely death has left a deep void in the lives of all the people who loved him, especially his little son and pregnant wife... He will be greatly missed by his parents, brother and everyone he touched," the obituary on the memorial funeral home's website read.
A 'Dr Vajinder Toor Memorial Fund' has been set up in his memory.