Allied pilot shot on the ground by Luftwaffe pilot after being shot down in aerial combat

[jiri]

After the end of WW2, in 1947 Oberst Joseph Priller (ex Kommodore JG 26) was imprisoned by Allied justice and accused that on the ground he shot an Allied pilot who was shot down in aerial combat and was captured unharmed.
Accusations against Priller were later dropped and he was released from prison.
Such an episode is likely to actually occur, even if the perpetrator was therefore not Priller.
Does somebody, please, the date and place of the incident and also the name of the murdered pilot? The pilot should have a Slavic name (possibly Polish or Czech). Nothing more are known for me at the moment.
Source: Josef Priller: Geschichte eines Jagdgeschwaders (JG 26).Vowinckelverlag, 1956.