The two women have been transferred to the Mansilla de las Mulas prison near the city of León where Carrasco, Spain's 20 minutos newspaper reported.

They have also been placed on suicide watch, according to Spanish news agency Efe. 

The mother, María Montserrat González Fernández, on Wednesday confessed to firing the bullets the killed the politician. She said she had done so because of a "personal grudge" after her daughter lost a wage dispute with the council Carrasco oversaw.

Police on Wednesday said the pair had planned the murder, doing practice runs up to five times, Spain's El País newspaper reported.

A third person — a policewoman and friend of the daughter — was also detained after she handed in a bag contained the murder weapon to authorities.

She denies knowing what was inside the bag, but police are questioning her involvement given she waited some 24 hours before handing in the bag.

Monday's killing has shocked Spain, with Prime Minister Marian Rajoy decrying it as a "wretched crime".

On Tuesday, mourning relatives wept outside a public building where Carrasco's body lay in state, attended by Rajoy and other leading politicians, while thousands of people filed past the politican's casket to pay their final respects.

Don't miss stories about Spain, join The Local on Facebook and Twitter.