For he had heard that they were ready to hand over the stronghold to the men whom Demetrius had sent: This first half of the verse continues the thought of the previous one, and can be connected to it as one sentence. Good News Bible does this fairly well, but we prefer the following model:

• He then quickly moved on to Joppa and captured it, 34 because he had heard [or, someone had told him] that the people there were planning to hand over the fortified city to Demetrius’ men.

And he stationed a garrison there to guard it may be rendered “He stationed [or, left] some of his soldiers there to guard it.”

Quoted with permission from Bullard, Roger A. and Hatton, Howard A. A Handbook on 1-2 Maccabees. (UBS Helps for Translators). New York: UBS, 2011. For this and other handbooks for translators see here.