Say:
on the head with a hammer
Suggestions in blue.

Originally Posted by
new2grammar
In a sensational revelation at the press conference, the Nodia Police said that the renewed dentist Dr. Rajesh is the murdered of her 14-year-old daughter.
In a sensational revelation at the press conference, the Nodia Police said that Dr. Rajesh, a dentist, is the murderer of his 14-year-old daughter.
I couldn't make sense out of "renewed" there, so I took it out.

Originally Posted by
new2grammar
Police theory says that Dr. Rajesh was having an extra-marital affair with his colleague Dr. Anita with which her daughter was uncomfortable.
Police theory says that Dr. Rajesh was having an extra-marital affair with his colleague Dr. Anita, and his daughter disapproved of it.

Originally Posted by
new2grammar
Secondly her daughter was having a close relation with the servant.
Secondly, his daughter was having an affair with the servant.

Originally Posted by
new2grammar
That fateful night when he returned home he found servant in her daughter’s room in an objectionable position but not compromising position. He took servant on the terrace on pretext he want to talk something important, there he hit him on head with hammer and then slit his throat.
That fateful night when he returned home he found the servant in his daughter’s room doing somethig objectionable. He took servant onto the terrace on the pretext that he want to talk about something important.

Originally Posted by
new2grammar
After that he came downstairs fixed a whisky for himself and went inside his daughter’s room and killed her in the same way. The Police said motive can be a ‘honour killing’ but that will be ascertain only after further investigation.

Originally Posted by
new2grammar
After that he came downstairs and poured a whisky for himself. Then he went inside his daughter's room and killed her the same way he had killed the servant. The Police said motive could be a ‘honour killing’ but that will be ascertained only after further investigation.
You need to more consistent with your descriptives (his, her).