The body of maid Rakhi, with several injury marks on her legs, chest and arms, was recovered from Singh's residence at South Avenue here last evening after the MP himself informed the police.
Jagriti was taken into custody this morning and questioned for 12 hours, investigators said.
An FIR was registered against her at Chankyapuri police station under sections 302 (murder), 307 (attempt to murder), 344 (wrongful confinement) of Indian Penal code and Juvenile Justice Act. Police are mulling to add sections under Bonded Labour Act for hiring a juvenile.
Former Bihar CM Lalu Prasad has been arrested recently over the fodder scam
Police claimed the maid died due to injuries inflicted by the MP's wife around 8.30 on Monday morning, but the matter was reported by BSP MP to police only at 8.30pm.
They said the injury marks were visible on arms, legs and chest. Police are also questioning Dhananjay to ascertain his role in the case.
Another minor help, who has been working at the household for the last one year, told police that he was also beaten up badly by Jagriti.
"The maid must have been beaten up mercilessly as her body bore several old and fresh injury marks," said a senior police official.
Dhananjay told police that he was away in his constituency Jaunpur in Uttar Pradesh and reached Delhi only in the evening and subsequently informed police, said investigators.
Jagriti has called Dhananjay and informed him about the maid's death, police said.
Rakhi had been working at the MP's residence for the last 10 months. According to police sources, Jagriti had been allegedly torturing her maid during this period.
"Although she was torturing her for past many months, but the frequency of beating had gone up since November 1," said a senior police officer.
BJP MP from Gujarat arrested for RTI activist's murder
The CBI on Tuesday arrested BJP MP from Gujarat Dinu Bogha Solanki in connection with the murder of of RTI activist Amit Jethwa who had waged a crusade against illegal mining in Gir Forest in the state, the last home of Asiatic lions.
Solanki, Lok Sabha member from Junagarh, Gujarat, arrived at the CBI headquarters this morning and was questioned throught the day, after which a CBI team decided to place him under arrest.
CBI spokesperson Kanchan Prasad said "the Lok Sabha MP from Junagadh has been taken into custody in the case of murder of RTI activist Amit Jethwa.
"He will be produced in a Delhi court tomorrow. Probe in the case is in progress", he added.
CBI sources said the parliamentarian was unable to give satisfactory answers after which it was decided to place him under arrest.
Gujarat Police had arrested six persons, including Shiva Solanki, nephew of the BJP MP, and sharp shooter Sailesh Pandya who had shot at Jethwa outside the Gujarat High Court. All of them were questioned by CBI inside a jail after taking permission from the designated court.
Jethwa was an RTI and environment activist who had filed numerous RTI applications and a PIL against illegal mining in Gir forest region. He was shot dead on July 20, 2010.
The MP was confronted with the statements given by other arrested accused in the case.
The BJP MP had been given a clean chit by Crime Branch of Gujarat Police prompting the father of the deceased to approach the Gujarat high court.