India’s ruling party has expelled an official accused of rape, days after a deadly car crash left his alleged victim in critical condition.

Investigators are examining possible links between Kuldeep Singh Sengar, a Bharatiya Janata party (BJP) lawmaker, who was accused of raping a teenage girl, and the collision that occurred on Sunday.

Two of the girl’s relatives were killed when a truck collided with their vehicle. The girl’s lawyer was also seriously injured. Images from the scene, broadcast on Indian media, showed that the truck’s number plates had been painted over.

The authorities in BJP-ruled Uttar Pradesh, one of India’s poorest states, have been accused of failing to protect the girl or fairly investigate claims made against the powerful official.

The BJP has also faced increasing criticism for allowing Singh Sengar to remain in the party, despite being charged under child protection laws last year. Officials said he had previously been suspended, but did not specify when this action was taken.

The girl alleged she was raped by Singh Sengar in June 2017 after going to his house looking for a job. For months the police refused to register a complaint, according to the family.

Kuldeep Singh Sengar. Photograph: Reuters

In protest at their lack of action, the girl travelled to Lucknow, the state capital of Uttar Pradesh, doused herself in paraffin and attempted to self-immolate. A day later, her father died in police custody. The family claimed he had been beaten by Singh Sengar and his brother.

After public outrage, Singh Sengar was arrested last year and has remained in custody. He has denied the allegation of rape and any involvement in the car crash.

The girl’s mother said the family had continued to receive constant threats and described Sunday’s collision as “a conspiracy to eliminate all of us”. The police initially said it appeared to be an accident, but federal investigators later said it may have been murder.

On Wednesday, the supreme court transferred all cases linked to the alleged rape to Delhi, a damning indictment of the justice system in Uttar Pradesh, which has a reputation for lawlessness.

The chief justice of India, Ranjan Gogoi, ruled that the country’s Central Bureau of Investigation, which is investigating the crash, must complete its inquiry in seven days, and the rape case in 45 days, according to reports.

He also said compensation should be paid to the girl, and that she could be moved to Delhi for treatment, if the family wished. She remains unconscious and in critical condition with a head injury and multiple leg fractures.

The case has caused outrage across India, with many arguing that justice systems offer little protection to vulnerable people who accuse the powerful. It has also prompted warnings about the handling of rape allegations, of which there are nearly 40,000 reported each year.

Campaigners say that while Indian laws against sexual assault have improved in recent years – prompted by a 2012 Delhi gang rape which became a catalyst for reform – victims still suffer humiliation when reporting and officials are often reluctant to register complaints.