Raggi's head of personnel Raffaele Marra arrested on suspicion of corruption.
Rome city personnel chief Raffaele Marra, the right-hand man to mayor Virginia Raggi, was arrested on 16 December on suspicion of corruption.
Police detained Marra together with large-scale property developer Sergio Scarpellini as part of an investigation into real-estate irregularities.
Marra is suspected of accepting funds from Scarpellini, which he allegedly used to buy his apartment, according to sources quoted in Italian daily newspaper Corriere della Sera.
The probe reportedly relates to property transactions in 2013 when Marra was Rome's head of housing policy under the administration of former mayor Gianni Alemanno.
Marra is considered a controversial figure within Raggi's anti-establishment Movimento 5 Stelle (M5S) on account of his close previous connections to right-wing figures Alemanno and former Lazio governor Renata Polverini.
Scarpellini is a powerful landlord in Rome and has amassed some €600 million over the last 15 years from rents paid by Italian parliamentary and senate bodies, as well as receiving a combined annual rent of about €14 million from the Comune di Roma, according to Corriere della Sera.
Marra's detention comes days after Rome's environment councillor Paola Muraro stood down, pending the outcome of an investigation for alleged environmental crimes. Muraro, for 12 years a consultant with the capital’s waste management company AMA Roma, will be heard by prosecutors on 21 December.
It comes a day after police searched city hall offices and seized records about disputed appointments by Raggi. The mayor said she had “nothing to hide” while the incident was brushed off the search as a "bufala" by the outspoken leader of M5S, Beppe Grillo.
Marra's suspected murky dealings with Scarpellini will likely increase the media glare on M5S which prides itself on being the “clean” alternative to mainstream Italian political parties.
It is also likely to heap pressure on Raggi who three months ago lost her cabinet chief and budget councillor as well as top managers of transport company ATAC and the head of AMA Roma.