Robberfly with Robberfly prey

Robberfly with Robberfly prey

Observation - Robberfly with Robberfly prey - UK and Ireland. Description: This Violet black-legged robberfly (Dioctria atricapilla) seems to have caught a much smaller robberfly by the hindlegs (or the smaller one chose the wrong target and had the tables turned...) - but what is the smaller one? A Leptogaster sp. I think, but

This Violet black-legged robberfly (Dioctria atricapilla) seems to have caught a much smaller robberfly by the hindlegs (or the smaller one chose the wrong target and had the tables turned...) - but what is the smaller one? A Leptogaster sp. I think, but which one - cylindrica or guttiventris?