His hand was in the trespass/ he had a hand in the crime/ to be guilty/ to be an accomplice
He was an accomplice to the forbidden act. He was responsible for the crime that was committed (from the point of view of the accused).
("For they had taken of their daughters for themselves and for their sons, so that the holy seed had mingled with the peoples of the lands; and the hand of the princes and the officials was foremost in this trespass" - Ezra 9:2; and also: "There are some among the supporters of the Zionist idea who do acts of frivolity and foolishness. For this reason our opponents decide that this idea has a hand in the wrongdoing" - Y. Reyns / Or Chadash Al Tzion)
Translation
Expression (Hebrew)
יָדוֹ בַּמַּעַל, יָדוֹ הָיְתָה בַּמַּעַל
Definition (Hebrew)
הָיָה שֻׁותָּף לַמַּעֲשֶׂה הָאָסוּר. הָיָה אַחְרַאי לַפֶּשַׁע שֶׁנַּעֲשָׂה (מֵעַל מַשְׁמָע מְעִילָה).
("כִּי נָשְׂאוּ מִבְּנֹתֵיהֶם לָהֶם וְלִבְנֵיהֶם וְהִתְעָרְבוּ זֶרַע הַקֹּדֶשׁ בְּעַמֵּי הָאֲרָצוֹת וְיַד הַשָּׂרִים וְהַסְּגָנִים הָיְתָה בַּמַּעַל הַזֶּה רִאשׁוֹנָה"- עֶזְרָא ט ב, וְכֵן:"יֵשׁ מֵהַמַּחְזִיקִים בְּרַעְיוֹן הַצִּיּוֹנִי שֶׁעוֹשִׂים דִּבְרֵי הוֹלֵלוּת וְשִׂכְלוּת. לְזֹאת מַחֲלִיטִים מִתְנַגְּדֵנוּ כִּי יַד הָרַעֲיוֹן הַזֶּה בַּמַּעַל"- י.רַיְנְס/ אוֹר חָדָשׁ עַל צִיּוֹן)