The Devyani case is all over the news. Over a thing like not paying her maid enough and stating her maid's pay wrongly in USA visa application. She is arrested, handcuffed, stripped and "cavity searched".
Arising from that, news media have explained the different classes of immunity.
According to the TV news, the ambassador personally has full diplomatic immunity. But not the consular staff.The US state department said that Ms Khobragade does not have full diplomatic immunity. It said under the UN's Vienna Convention on Consular Relations, she is immune from arrest only for crimes committed in connection with her work.
According to the above, a chargé d'affaires , such as for example Ionescu, who is NOT the ambassador; does not have full diplomatic immunity. Especially if he killed some person with his car. Perhaps carousing in KTV nightclub with Korean married woman and sending her back cannot be consular work. He flew back to Romania.